Vent stack needed for toilet only?

[GCarnegi]

I am installing a new downstairs WC and am wondering if I need a vent stack, or stink pipe, if ALL that I have on the drain is the toilet.

The sink is drained separately as it would have been awkward to tie it into the toilet waste.

There is a bedroom above the WC, so no additional drainage is required into the toilet waste from anywhere else in the house.

If I DO need a vent stack, then assuming there is no waste water ever flowing in it (above where the toilet waste enters it) then does it really need to be a 110mm pipe? As this pipe will only be used for an air inlet during flushing, or a vent for the sewer gas at other times, then can I change over to a 68mm vertical pipe, or for that matter 50, 40, 30 or 22mm.

thanks

 

[HotrodCJH]

Have you thought about using an AAV (Automatic Air Vent). This would allow for venting of the stack without having to take it all the way up through the roof.

I think it is common practice to then use a 4"AAV or reduce to 3"pipe and a 3"AAV.

However if the water runs quickly away and there are few restrictions in the pipe work, you may get away with not having one at all.
Not the best practice but could work.

 

[Kev F]

If there's another stack in the house that it's connected to you won't need any thing, just drop it straight into floor.

 

[GCarnegi]

The loo is about four or five feet away from the main drain that runs through my back garden, (runs along the back of this row of terraced houses) so there should be no restriction whatsoever between the loo and the main drain (apart from this 5ft of 110mm pipe) (the loo is against the back wall of the house, and the main terrace drain runs underground approx 4ft behind the row of houses.

There is another vent stack in the house from the upstairs toilet in the other half of the house which connects to that main drain separately (further along), but this is about 20ft feet away horizontally, so tying back to that from this toilet would be really awkward if not impossible.

I guess I should probably just try it without a vent stack, and if I hit problems, then swap out the 90 degree bend where the pipe exits the house wall for a tee piece, and run my stack upwards from there, up the outside of the house.

 

[Hugh Jaleak]

A ground floor W.C. can be directly connected to the drain provided the distance between the crown of the W.C. trap and the invert of the drain doesn't exceed 1.3m. Dont think you'll have any problems which what you describe provided the existing drain isn't ridiculously deep.

Make sure the new drain is accessible for rodding through to the existing run, and check with Building Control, you will probably need permission to connect to the existing drain.